This invention relates generally to a fluid loss measuring system and method and particularly, but not by way of limitation, to such a system and method in which the amount of fluid loss is automatically sensed and indicated to a computer.
In the oil and gas industry, different types of fluids can be pumped into a well for various purposes. For example, a cement slurry can be pumped in a well to secure tubular casing for supporting the well bore, and a fracturing fluid can be pumped through a well into a geological formation to open it for improving flow of oil or gas into the well. Because these fluids typically come into contact with one or more porous subterranean formations, at least part of such fluids can leak off into the formations. Such fluid loss can be expensive, both because more fluid has to be put downhole to achieve the desired function for which the lost fluid is unavailable and because the lost fluid can damage the formation such that it is rendered less productive. Furthermore, such fluid loss can adversely affect the nature of the fluid as different constituents of the fluid can leak off in varying amounts such that the relative concentrations within the remaining fluid are different from the designed and originally pumped in fluid.
To try to overcome the fluid loss problem, fluid loss tests can be run to determine how much loss is likely to occur and whether one type of fluid is less susceptible to leak off than another. In one type of fluid loss test, a core sample from a formation is placed in a fluid loss cell having an inlet and an outlet. The fluid to be tested is introduced, such as by being pumped, into the fluid loss cell. Typically this occurs under pressure, such as can be imparted by steam or nitrogen, for example. The fluid can be held in the cell or flow through it.
The fluid contacts the core sample, which acts as a filter due to its inherent porosity, and any fluid loss through the sample is retrieved through the outlet of the fluid loss cell. The collected fluid is typically manually measured, such as in a graduated cylinder disposed below the outlet of the cell.
A phenomenon of such a test is known as "blow off." This occurs when the core sample (or other type of filter) becomes depleted whereupon exiting gases cause rapid increase in pressure. The timing of this typically cannot be predetermined so that a safety problem can occur due to the rapid pressure output occurring at an unknown time. Blow off also changes the rate of fluid loss so that if the entire test is not carefully monitored, incremental quantities and rates of fluid loss will not be known since they are not constant.
Another aspect of fluid loss testing in the oil and gas industry is that it is becoming more and more automated with the advent of microprocessor-based computers. The aforementioned manual technique of taking fluid loss readings does not provide input directly into any such computer.
To overcome the foregoing shortcomings of the aforementioned fluid loss testing of which we are aware, there is the need for a fluid loss measuring system and method in which the fluid from the fluid loss occurring through a selected filter in a fluid loss cell is automatically sensed and indicated, preferably in a manner adapted for direct input and use by a computer that may be controlling aspects of the fluid loss test. Such a system and method should be able to contain and respond to a blow off condition.